Method and apparatus for allocating ackch resources in a wireless communication system

ABSTRACT

A method for allocating physical resources to an Acknowledgement (ACK)/Negative Acknowledgement (NACK) signal channel representative of a response signal in a wireless communication system. The method includes grouping ACK/NACK signal channels corresponding to a plurality of resource blocks used for transmission of a data channel or a control channel into a plurality of groups so ACK/NACK signal channels having consecutive indexes do not belong to the same group; and allocating same frequency resources to ACK/NACK signal channels belonging to the same ACK/NACK signal channel group and allocating orthogonal sequences so ACK/NACK signal channels in each ACK/NACK signal channel group are distinguished in a code domain.

PRIORITY

This application claims priority under 35 U.S.C. § 119(a) to a KoreanPatent Application filed in the Korean Intellectual Property Office onApr. 26, 2007 and assigned Serial No. 2007-41034, the disclosure ofwhich is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to a resource allocation methodand apparatus for a wireless communication system, and in particular, toa method and apparatus for allocating positive Acknowledgement(ACK)/Negative Acknowledgement (NACK) physical channel, referred toherein as ACKCH, resources with which a reception side notifies atransmission side of the success/failure in decoding of a received datachannel.

2. Description of the Related Art

In wireless communication systems, the technology for controlling atransmission error during data transmission is generally classified intoa Forward Error Correction (FEC) technique and an Automatic RepeatreQuest (ARQ) technique. The FEC technique attempts to correct an errordetected from received data, and decodes correct data upon success inthe error correction. However, when the FEC technique has failed in theerror correction, wrong information may be provided to users or theinformation may be missing. The ARQ technique transmits data using anFEC code having a high error detection capability, and when an error isdetected from received data, a reception side sends a request for dataretransmission to a transmission side.

The FEC technique has a relatively lower efficiency in a good channelenvironment, and reduces system reliability when the FEC technique failsin the error correction. On the contrary, the ARQ technique typicallysecures high system reliability and enables efficient transmission witha low redundancy, but the system reliability is considerably reduced ina poor channel environment due to the frequent retransmission request.In order to address such shortcomings, the two techniques have beenappropriately combined to provide a Hybrid ARQ (HARQ) technique.

The HARQ technique basically attempts error correction on received codeddata, referred to herein as a HARQ packet, and determines whether tomake a retransmission request for the HARQ packet using a simple errordetection code, such as a Cyclic Redundancy Check (CRC) code. Areception side of a system using the HARQ technique determinespresence/absence of an error in a received HARQ packet, and transmits anHARQ Positive Acknowledgement (ACK) signal or an HARQ NegativeAcknowledgement (NACK) signal to a transmission side according to thepresence/absence of an error. The transmission side performsretransmission of the HARQ packet or transmission of a new HARQ packetaccording to the HARQ ACK/NACK signal. Upon normal receipt of an HARQpacket, the reception side transmits the ACK/NACK signal usingappropriate resources. Particularly, when the HARQ technique is used, achannel over which the ACK/NACK signal is transmitted is called aPhysical Hybrid ARQ Indicator Channel (PHICH).

An Orthogonal Frequency Division Multiplexing (OFDM)-based wirelesscommunication system transmits the ACK/NACK signal on severalsubcarriers, and a Wideband Code Division Multiple Access (WCDMA) systemtransmits the ACK/NACK signal on a particular code channel. Generally,since packet data for several users is simultaneously transmitted in anarbitrary packet data transmission interval or Transmission TimeInterval (TTI), ACKCHs for each of the HARQ packets are transmitted atparticular times after the data received from the users which arescheduled data in the TTI is decoded.

Transmission of the ACKCH will be considered below separately for thedownlink and the uplink. Regarding ACKCH for downlink data channels,each terminal or User Equipment (UE) that has received each of the datachannels from a base station is allocated physical channel resources fortransmitting the ACK/NACK signal from the base station, and transmitsthe ACKCH on the uplink. Meanwhile, regarding ACKCH for uplink datachannels, after a base station receives the data channels fromcorresponding UEs, the base station transmits ACKCH for each data packetover the resources agreed upon between the base station and each UE.

FIG. 1 illustrates a conventional OFDM-based downlink frame structure ofEnhanced Universal Terrestrial Radio Access (EUTRA) which is the nextgeneration mobile communication standard of the 3rd GenerationPartnership Project (3GPP). Referring to FIG. 1, a total of 50 ResourceBlocks (RBs) 102 exist in a 10-MHz system bandwidth 101. One RB iscomposed of 12 subcarriers 103, and can have 14 OFDM symbol intervals104. In every OFDM symbol interval 104, a modulation symbol of adownlink channel is transmitted on each subcarrier 103. As shown above,one subcarrier band in one OFDM symbol interval is referred to as aResource Element (RE) 106, and in FIG. 1, a total of 168 (=14 OFDMsymbols×12 subcarriers) REs exist in one RB. In one OFDM symbol interval104, one downlink data channel can be allocated to one or more RBsaccording to a data rate, and can be transmitted through the allocatedRBs.

With consideration of the downlink frame structure of FIG. 1, a maximumof 50 downlink data channels can be simultaneously scheduled in one TTI105. In this case, the uplink needs 50 ACKCHs. Generally, a group ofmultiple REs 106 constitutes one ACKCH, and the overhead and performanceoccupied by the ACKCH in all resources of the system depends on howresources of the ACKCH are formed.

Therefore, in order to improve the overhead and performance occupied byACKCH in all resources of the system, a need exists for a scheme forefficiently allocating and forming resources of the ACKCH.

SUMMARY OF THE INVENTION

The present invention substantially addresses at least theabove-described problems and/or disadvantages and provides at least theadvantages described below. Accordingly, an aspect of the presentinvention is to provide an ACKCH resource allocation method andapparatus capable of improving reception performance of an ACKCH whenthe ACKCH has an implicit mapping relation with RBs used fortransmission of a data channel, or when the ACKCH has an implicitmapping relation with control channel resources used for transmittingscheduling information of the data channel in a wireless communicationsystem.

Another aspect of the present invention is to provide an ACKCH resourceallocation method and apparatus capable of uniformly allocatingfrequency resources for a downlink ACKCH and achieving good frequencydiversity and inter-cell interference diversity when ACKCH has animplicit mapping relation with RBs used for transmission of a datachannel in a system where consecutive RBs are allocated for one datachannel, like the Single-Carrier Frequency Division Multiple Access(SC-FDMA) system.

A further aspect of the present invention is to provide an ACKCHresource allocation method and apparatus capable of allowing ACKCHs tobe transmitted without interference between ACKCHs when multiple ACKCHsuse RBs used for transmission of a data channel by means of Multi-UserMulti-Input Multi-Output (MU-MIMO) transmission in the case where theACKCHs have an implicit mapping relation with the RBs used fortransmission of the data channel in a system where consecutive RBs areallocated for one data channel.

According to an aspect of the present invention, there is provided amethod for allocating physical resources to an ACK/NACK signal channelrepresentative of a response signal in a wireless communication system.The method includes grouping ACK/NACK signal channels corresponding to aplurality of resource blocks used for transmission of a data channel ora control channel into a plurality of groups so ACK/NACK signal channelshaving consecutive indexes do not belong to the same group; andallocating same frequency resources to ACK/NACK signal channelsbelonging to the same ACK/NACK signal channel group and allocatingorthogonal sequences so ACK/NACK signal channels in each ACK/NACK signalchannel group are distinguished in a code domain.

According to another aspect of the present invention, there is provideda method for allocating physical resources to an ACK/NACK signal channelrepresentative of a response signal in a wireless communication system.The method includes decoding a data channel and a control channelreceived through a plurality of resource blocks; generating an ACK/NACKsymbol according to success/failure in the decoding; grouping ACK/NACKsignal channels corresponding to the resource blocks into a plurality ofgroups according to a number of and indexes of the resource blocks soACK/NACK signal channels having consecutive indexes do not belong to thesame group; allocating same frequency resources to ACK/NACK signalchannels belonging to the same ACK/NACK signal channel group andallocating orthogonal sequences so ACK/NACK signal channels in eachACK/NACK signal channel group are distinguished in a code domain; andmultiplying the generated ACK/NACK symbol by a sequence allocated to anACK/NACK signal channel for transmitting the generated ACK/NACK symbol,to spread the generated ACK/NACK symbol.

According to a further aspect of the present invention, there isprovided an apparatus for allocating physical resources to an ACK/NACKsignal channel representative of a response signal in a wirelesscommunication system. The apparatus includes a channel decoder fordecoding a data channel and a control channel received through aplurality of resource blocks; an ACK/NACK symbol generator forgenerating an ACK/NACK symbol according to success/failure in thedecoding by the channel decoder; an ACK/NACK signal channel formatcontroller for grouping ACK/NACK signal channels corresponding to theresource blocks into a plurality of groups according to a number of andindexes of the resource blocks so ACK/NACK signal channels havingconsecutive indexes do not belong to the same group, allocating samefrequency resources to ACK/NACK signal channels belonging to the sameACK/NACK signal channel group, and allocating orthogonal sequences soACK/NACK signal channels in each ACK/NACK signal channel group aredistinguished in a code domain; and a spreader for multiplying thegenerated ACK/NACK symbol by a sequence allocated to an ACK/NACK signalchannel for transmitting the generated ACK/NACK symbol, to spread thegenerated ACK/NACK symbol.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features and advantages of the presentinvention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a diagram illustrating a conventional OFDM-based downlinkframe structure;

FIGS. 2A and 2B are diagrams illustrating an example where ACKCHresources have an implicit mapping relation with a data channel or ascheduling control channel according to the present invention;

FIG. 3 is a diagram illustrating an ACKCH resource allocation methodaccording to a first embodiment of the present invention;

FIG. 4 is a diagram illustrating a process of mapping multiple ACKCHs tothe same RE group according to the first embodiment of the presentinvention;

FIGS. 5A and 5B are diagrams illustrating a situation in which downlinkchannels are mapped to REs separately for each cell according to thefirst embodiment of the present invention;

FIG. 6 is a control flow diagram illustrating an ACKCH transmissionprocedure of a transmission apparatus of a base station according to thefirst embodiment of the present invention;

FIG. 7 is a control flow diagram illustrating an ACKCH receptionprocedure of a reception apparatus of a UE according to the firstembodiment of the present invention;

FIG. 8 is a diagram illustrating a structure of the transmissionapparatus of the base station of FIG. 6 according to the firstembodiment of the present invention;

FIG. 9 is a diagram illustrating a structure of a reception apparatus ofa UE of FIG. 7 according to the first embodiment of the presentinvention;

FIG. 10 is a diagram illustrating a format example of a schedulingchannel for uplink MU-MIMO transmission according to a second embodimentof the present invention;

FIG. 11 is a diagram illustrating an ACKCH transmission procedure of abase station according to the second embodiment of the presentinvention; and

FIG. 12 is a diagram illustrating an ACKCH reception procedure of a UEaccording to the second embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will now be described indetail with reference to the annexed drawings. In the followingdescription, a description of known functions and configurationsincorporated herein has been omitted for clarity and conciseness. Termsused herein are based on functions in the present invention and may varyaccording to users, operators' intention or usual practices. Therefore,the definition of the terms should be made based on contents throughoutthe specification. In particular, Acknowledgement (ACK)/NegativeAcknowledgement (NACK) physical channel (ACKCH) and Physical HybridAutomatic Repeat reQuest Indicator Channel (PHICH) used throughout thisdisclosure each indicate a channel over which an ACK/NACK signal istransmitted.

Although embodiments of the present invention will be described belowmainly for an Orthogonal Frequency Division Multiplexing (OFDM)-basedwireless communication system, especially for the 3^(rd) GenerationPartnership Project (3GPP) Enhanced Universal Terrestrial Radio Access(EUTRA) standard, those skilled in the art should understand that thepresent invention can be applied to other communication systems havingthe similar technical background and channel format with a slightmodification without departing from the spirit and scope of theinvention.

The present invention provides a method and apparatus for allocatingresources for ACKCH in a wireless communication system. FIGS. 2A and 2Bare diagrams illustrating an example where ACKCH resources have animplicit mapping relation with a data channel(s) or scheduling controlchannel(s). According to the present invention, as shown in FIGS. 2A and2B, when ACKCH resource #1 201 has an implicit mapping relation withRB#1 202 used for transmission of a data channel or when ACKCH resource#1 203 has an implicit mapping relation with downlink Control ChannelElement (CCE) 204 where data transmitted over the data channel isscheduled, the ACKCH resources existing in several frequency domains inthe system band are uniformly used without being concentrated on aparticular frequency domain. Implicit mapping, as used herein, refers topre-defined mapping, and indicates that a UE, when transmitting orreceiving an ACK/NACK channel, can determine which resource the UEshould use, through use of pre-defined mapping between ACK/NACK channelresource and data channel RB or pre-defined mapping between ACK/NACKchannel resource and scheduling control channel, without the need toexplicitly receive signaling information from a base station.

In addition, the present invention maps an ACKCH to a physical resourceto improve frequency diversity gain and inter-cell interferencediversity gain.

Further, the present invention uses the same Resource Block(s) (RB(s))during Multi-User Multi-Input Multi-Output (MU-MIMO) transmission soACKCHs from MU-MIMO User Equipments (UEs) receiving transmission datacan be transmitted to a base station without mutual interference. Inparticular, the present invention brings performance improvement ofACKCH and efficient utilization of resources when a technology isapplied in which multiple ACKCHs are transmitted after being mapped tothe same frequency resource using Code Division Multiplexing (CDM).

An ACKCH resource allocation method and apparatus for a wirelesscommunication system according to the present invention implicitlysignals physical resources to be used for the ACKCH through use of amapping relation preset between resources allocated to the data channeland resources allocated to the ACKCH, or between a downlink controlchannel where the data channel is scheduled and resources allocated tothe ACKCH.

Regarding physical resources, i.e., a set of Resource Elements (REs), tobe used for transmission of each ACKCH, the base station can explicitlyprovide corresponding information to a UE, or can allow the set of REsto be used for ACKCH transmission to have an implicit mapping relationwith an RB used for transmission of a downlink data channel or withdownlink CCE where data resources are scheduled, as shown in FIGS. 2Aand 2B.

More specifically, referring to FIGS. 2A and 2B, the present inventionmaps physical resources to an ACKCH, when an implicit mapping rule isapplied between an ACKCH and an RB of a data channel, or between anACKCH and a downlink CCE. The core of the physical resource mappingmethod is to map ACKCHs being mapped to consecutive RBs or CCEs withconsecutive indexes, to different frequency resources. The mappingprocess allows REs used for transmission of the ACKCHs to uniformlyspread over the entire system band, so the ACKCH resource allocationmethod and apparatus according to the present invention can uniformlyuse frequency resources of ACKCHs and achieve good frequency diversityand inter-cell interference diversity in the system where consecutiveRBs are allocated for one data channel, like a Single-Carrier FrequencyDivision Multiple Access (SC-FDMA) system.

As shown in FIGS. 2A and 2B, when implicit mapping is used, the basestation has no need to explicitly signal ACKCH resources to a UE,contributing to a considerable reduction in or removal of signalingoverhead of ACKCH resources. Shown in FIG. 2A is an example where ACKCHresources are mapped to N RBs on a one-to-one basis. Each ACKCH resource201 in FIG. 2A is one physical channel composed of several REs 106 inFIG. 1, and when transmission of several ACKCHs is permitted through thesame REs 106, they are different ACKCH resources 201 since they aredifferent in CDM sequence used for distinguishing each ACKCH. If a UEtransmits a data channel using RB#1 202, an ACKCH for the UE istransmitted from the base station using ACKCH resource #1 201 and the UEreceives the corresponding ACKCH.

Meanwhile, shown in FIG. 2B is an example where ACKCH resources areimplicitly mapped to CCE 204 of a downlink control channel fortransmitting scheduling information of the data channel. In the above,CCE 204 indicates a set of REs 106 constituting the downlink controlchannel. For example, a UE, which is scheduled (allocated) an uplinkdata channel from a control channel based on CCE#1 204, transmits anACK/NACK signal using ACKCH resource #1 203 mapped to the CCE#1 204. Thedownlink control channel can be composed of one or multiple CCEsaccording to the channel state of the UE receiving the control channel,and the amount of information transmitted over the control channel.

A description will now be made of an ACKCH resource mapping andsignaling technology according to the present invention.

FIG. 3 is a diagram illustrating an ACKCH resource allocation methodaccording to a first embodiment of the present invention. In the firstembodiment of the present invention, RBs 302 are allocated during datachannel transmission in the uplink, REs 301 are used for ACKCHtransmission for the uplink data channel in the downlink, and theremaining downlink REs are not shown for convenience.

Meanwhile, shown in FIGS. 5A and 5B is an example where REs 501, 502 and503 used for transmission of ACKCH and REs 504, 505 and 506 used fortransmission of the remaining channels such as Physical Downlink ControlChannel (PDCCH) and Physical Downlink Shared Channel (PDSCH) areillustrated together. FIGS. 5A and 5B are diagrams illustrating thesituation in which downlink channels are mapped to REs separately foreach cell. REs denoted by reference numeral 306 and 309 in FIG. 3correspond to REs denoted by reference numeral 501 in FIGS. 5A and 5B;REs denoted by reference numeral 307 and 310 in FIG. 3 correspond to REsdenoted by reference numeral 502 in FIGS. 5A and 5B; and REs denoted byreference numeral 308 and 311 in FIG. 3 correspond to REs denoted byreference numeral 503 in FIGS. 5A and 5B.

In FIG. 3, since the horizontal axis 312 represents frequency, the REsspaced farther from each other are significantly different in frequencyon the downlink transmission band. As shown in FIG. 3, REs denoted byreference numeral 306 and REs denoted by reference numeral 311 arelocated in the opposite sides on the transmission band. Although adescription of the first embodiment is given herein as to downlink ACKCHfor an uplink data channel, the same can be applied even to uplink ACKCHfor a downlink data channel.

According to a mapping rule between uplink RB 302 and downlink ACKCH 301shown in FIG. 3, since downlink ACKCH for uplink data channeltransmitted using RB#1 is mapped to REs 306 and 309 (see 303), a basestation transmits an ACK/NACK signal using the REs 306 and 309 afterreceiving the data channel from a UE, and the UE receives ACK/NACKsignal from the REs through use of a particular mapping rule 303.Similarly, downlink ACKCH for the uplink data channel transmitted usingRB#2 is transmitted using REs 307 and 310. The REs 306 and 309, and theREs 307 and 310 preferably have bands spaced apart to some extent inorder to obtain frequency diversity gain.

The present invention is more advantageous to a case where more than twoconsecutive RBs are allocated for data channel transmission.Particularly, in the EUTRA uplink, since the SC-FDMA transmission schemeis used, consecutive RBs are usually allocated in order to satisfy thesingle-carrier transmission characteristic when more than two RBs areallocated for data channel transmission. For example, in FIG. 3, if RB#2and RB#3 are allocated for transmission of a certain data channel and aUE transmits the data channel using the RBs, a base station can use REs307, 308, 310 and 311 for ACKCH transmission by means of mapping rules304 and 305. In this case, if the base station receiving the datachannel transmits ACKCH using all the REs 307, 308, 310 and 311, anACK/NACK signal is distributed over four RE groups 307, 308, 310 and 311during transmission of the ACK/NACK signal, making it possible toimprove frequency diversity and inter-cell interference diversity gainsas several ACKCH frequency resources are uniformly used as compared withthe case where only the RE groups 307 and 310, or 308 and 311 mapped toone RB are used.

If several ACKCH frequency resources are uniformly used in this way,performance reduction caused by the mutual interference between ACKCHsmultiplexed to the concentrated frequency resources as ACKCHtransmission is concentrated only on particular frequency resources canbe prevented. Meanwhile, in this first embodiment, one RE group iscomposed of four adjacent REs, and the present invention is not limitedto an RE group having a specific size and can be applied regardless ofthe number of REs belonging to the RE group.

According to the mapping method shown in FIG. 3, when a data channel istransmitted using three arbitrary consecutive RBs, ACKCH can betransmitted using all of six RE groups 306˜311. For example, when RB#3,RB#4 and RB#5 are used for data channel transmission, all of ACKCHresources 315, 316 and 317 mapped to the three RBs are used, so theACKCH is distributed over six RE groups 306˜311 during transmission ofthe ACKCH. In this case, in each RE group, sequences allocated to theACKCH resources 315, 316 and 317 are used.

In addition, four ACKCH resources 313, 316, 319 and 320 exist in the REgroup 309 in order to transmit ACKCH mapped to RB#1, RB#4, RB#7 andRB#10, and the four ACKCH resources 313, 316, 319 and 320 aretransmitted over the same frequency resources. The four ACKCH resources313, 316, 319 and 320, as shown in FIG. 4, are allocated sequenceshaving mutual orthogonality or quasi-orthogonality separately for eachACKCH resource so they can be distinguished in the code domain.

FIG. 4 is a diagram illustrating a process of mapping multiple ACKCHs tothe same RE group according to the first embodiment of the presentinvention. For example, if an ACK/NACK signal to be transmitted isdefined as ‘b’ when a ACKCH mapped to a data channel transmitted on RB#1is transmitted, s11 xb, s12 xb, s13 xb and s14 xb are formed in the REgroup 309 by multiplying the ACK/NACK signal b by sequences 402 of s11,s12, s13 and s14, respectively, and transmitted over RE#1, RE#2, RE#3and RE#4, respectively. In the above process, the sequences 402 of s11,s12, s13 and s14 can be made by multiplying orthogonal sequences such aslength-4 Walsh or DFT sequences by cell-specific random sequences. Sincesequences having a long length are generally applied for thecell-specific random sequences, every RE group has a different sequencevalue.

Regarding ACKCH corresponding to a data channel transmitted on RB#7, anACK/NACK signal to be transmitted on the RE group 309 are multiplied bysequences 404 of s31, s32, s33 and s34, and transmitted on RE#1, RE#2,RE#3 and RE#4, respectively. Therefore, according to this firstembodiment, ACKCHs being mapped to RBs RB#1, RB#4, RB#7 and RB#10 spacedapart from each other can be transmitted by applying different sequencesto the same frequency resource, i.e., by applying CDM. This is becauseACKCHs belonging to consecutive RBs are mapped to different frequencyresources in FIG. 3.

Although an example where length-4 sequences are applied separately foreach RE group is shown in FIG. 3 and FIG. 4, if a real part and animaginary part separately carry one sequence chip during ACK/NACK signaltransmission, length-8 sequences can be applied. In this case, 8different ACKCHs can be transmitted on one RE group.

Meanwhile, FIG. 5A showing an example where ACKCH resources areallocated to several cells is an example where RE groups 306˜311allocated to ACKCH of FIG. 3, referred to herein as ACKCH RE groups, aremapped to physical resources at regular frequency intervals. That is, REgroups 501, 502 and 503 correspond to RE groups 306, 307 and 308 of FIG.3, respectively. The RE groups 501˜503 are spaced apart from each otherat intervals of two RBs. In FIGS. 5A and 5B, Cell#11, Cell#12 andCell#13 are cells belonging to the same base station, and similarly,Cell#21 and Cell#23 are also cells belonging to the same base station.However, Cell#11, Cell#21 and Cell#31 are cells belonging to differentbase stations. Aside from the RE groups 501˜503 for ACKCH transmission,FIGS. 5A and 5B show REs 504 and 505 mapped to a Reference Signal (RS)for channel estimation and REs 506 mapped to control channels and data.

According to the ACKCH transmission method shown in FIG. 3, ACKCHcorresponding to a data channel transmitted using three or morearbitrary consecutive RBs can always be transmitted using all of REgroups 501, 502, 503, making it possible to improve frequency diversitygain and inter-cell interference diversity gain as compared with thecase where only one of the RE groups 501˜503 is used. Similarly, whentwo consecutive RBs are allocated for data channel transmission, two REgroups among the RE groups 501˜503 are always selected for transmissionof ACKCH, making it possible to obtain improved performance.

Meanwhile, each ACKCH RE group shown in FIG. 5A has a cell-specificoffset to reduce interference between ACKCHs of different cells. Forexample, since Cell#11, Cell#12 and Cell#13 belong to the same basestation, ACKCHs from the cells are transmitted on different REs,preventing occurrence of mutual interference. However, since there is alimitation on the applicable offset value, there is a possible casewhere some ACKCHs from different cells use the same REs as done inCell#21 and Cell#31.

Shown in FIG. 5B is an example where the ACKCH RE groups 306˜311 havethe cell-specific random frequency interval. Therefore, while RE groupscorresponding to ACKCHs show a distance difference corresponding to thesame frequency offset between two arbitrary cells in FIG. 5A, aninterval between ACKCH RE groups is random in FIG. 5B, making itpossible to more randomize interference from ACKCHs of different cells.Even in FIG. 5B, regarding ACKCH RE mapping with RB in each cell, whenmore than two consecutive RBs are used for data channel transmission asdescribed above, at least two RE groups among the RE groups 501˜503 areused for ACKCH transmission, contributing to improvement of frequencydiversity, and since random inter-cell ACKCH RE mapping is applied, aninter-cell ACKCH interference randomization effect can further increase.

FIG. 6 is a control flow diagram illustrating an ACKCH transmissionprocedure of a transmission apparatus of a base station according to thefirst embodiment of the present invention. In the transmission procedureof FIG. 6, when multiple RBs are allocated to a data channel, the RBsare assumed to be consecutive to each other. In step 600, thetransmission apparatus of the base station determines an ACK/NACK valueaccording to the decoding result on a data channel received from a UE,and prepares to transmit an ACKCH signal. In step 601, the transmissionapparatus of the base station checks the number of RBs allocated to thereceived data channel, and when only one RB is allocated for the datachannel, the transmission apparatus of the base station maps an ACK/NACKsignal to an ACKCH RE group mapped to the RB in step 602. Thereafter, instep 603, the transmission apparatus of the base station multiplies theACK/NACK signal by a CDM sequence for each of the ACKCH resourcesseparately for each RE. Referring to FIG. 4, when RB#1 is allocated tothe data channel, a sequence allocated to ACKCH resource of acorresponding RE group is multiplied separately for each RE group asshown by reference numeral 402.

Since three different RE groups 501, 502 and 503 are defined asfrequency resources for transmitting ACKCH as shown in FIGS. 5A and 5B,the transmission apparatus of the base station determines in step 610whether the number of RBs allocated for transmission of the data channelis greater than three, and when two or three RBs are allocated to thedata channel, the transmission apparatus of the base station maps atransmission ACK/NACK signal to an ACKCH RE group mapped to the RBs instep 604. Referring to FIG. 3, when RB#2 and RB#3 are allocated to thedata channel, the transmission apparatus of the base station maps theACK/NACK signal to RE groups 307, 308, 310 and 311 mapped thereto. Whenthe number of sets of frequency resources for transmitting ACKCH is notthree, the number of RBs, which is a criterion for determination in step610, can be changed according thereto. Meanwhile, the number of RBs,which is a criterion for determination in step 610, can be set to tworather than three regardless of the number of sets. In this case, whenmultiple RBs are allocated to the data channel, the transmissionapparatus of the base station only needs to always use only two ACKCHresources regardless of the number of allocated RBs. In step 605, thetransmission apparatus of the base station multiplies each of RE groups,to which the ACK/NACK signal is mapped in step 604, by a correspondingCDM sequence.

However, if the base station determines in step 610 that the number ofRBs allocated to the data channel exceeds three, the transmissionapparatus of the base station selects ACKCH resources mapped to RBscorresponding to the first three indexes among the RBs in step 606.Referring to FIG. 3, when RB#2˜RB#7 are allocated to the data channel,ACKCH resources 314, 315 and 316 corresponding to RB#2, RB#3 and RB#4are selected. In step 607, the transmission apparatus of the basestation maps the ACK/NACK signal to the ACKCH resources selected in step606. In step 608, the transmission apparatus of the base stationmultiplies the ACK/NACK signal by CDM sequences corresponding to theACKCH resources separately for each RE group.

Thereafter, in step 609, the transmission apparatus of the base stationadjusts a transmission level of a signal on ACKCH RE according to thenumber of RE groups used for ACKCH channel transmission for the datachannel. For example, when the number of RBs allocated to the datachannel is three, the level is adjusted to ⅓, compared to when thenumber of RBs is one. This is to keep the total power of thetransmission ACKCH signal constant regardless of the number of RE groupsused for the ACKCH transmission. Finally, in step 611, the ACKCH signalis mapped to a corresponding Inverse Fast Fourier Transformer (IFFT)input of the transmitter separately for each RE allocated for the ACKCH,and then transmitted. The same transmission procedure can be appliedeven when the number of RBs allocated to the data channel, which is acriterion for determination in step 610, is set to two and ACKCHresources corresponding to the first two RBs are selected in step 606.

FIG. 7 is a control flow diagram illustrating an ACKCH receptionprocedure of a reception apparatus of a UE according to the firstembodiment of the present invention. In step 700, the UE prepares toreceive ACKCH from a base station after transmitting a previouslyscheduled data channel. Thereafter, the UE determines the number of RBsscheduled for the data channel in step 701, and if only one RB isallocated, the UE receives the ACKCH signal from the Fast FourierTransformer (FFT) outputs of the receiver corresponding to ACKCH REsmapped to the RB in step 702. In step 703, the UE despreads the ACKCHsignal received in step 702 using sequences corresponding to the ACKCHresources.

However, if the UE determines in step 701 that the number of RBsscheduled for the data channel is greater than one, the UE proceeds tostep 710 where the UE determines whether the number of RBs allocated tothe data channel is greater than three. If the number of allocated RBsis two or three, the UE proceeds to step 704 where the UE receives theACKCH signal from FFT outputs corresponding to the ACKCH REs mapped tothe RBs. Thereafter, in step 705, the UE despreads the ACKCH signalreceived in step 704 using sequences corresponding to the ACKCHresources.

However, if the UE determines in step 710 that the number of RBsallocated to the data channel is greater than three, the UE proceeds tostep 706 where the UE selects ACKCH resources mapped to the first threeRB indexes among the RBs. Thereafter, the UE receives an ACKCH signalfrom FFT outputs corresponding to the selected resources in step 707,and then despreads the received ACKCH signal using sequencescorresponding to the ACKCH resources in step 708. Thereafter, in step709, the UE determines whether an ACK/NACK signal is received from thedespread ACKCH signal.

FIG. 8 is a diagram illustrating a structure of the transmissionapparatus of the base station of FIG. 6 according to the firstembodiment of the present invention. An ACK/NACK symbol generator 801generates an ACK/NACK symbol for a data channel according to thedecoding success/failure result of a data channel decoder 805. Aspreader 802 multiplies the generated ACK/NACK symbol by a CDM sequencecorresponding to ACKCH resource allocated for transmission of theACK/NACK symbol to thereby spread the ACK/NACK symbol. Also, thespreader 802 performs scaling on a level of a transmission ACK/NACKsignal as done in step 609 of FIG. 6. An ACKCH format controller 806determines an ACKCH format, i.e., spreading gain and ACKCH resources fortransmission of ACKCH, according to the number of RBs allocated to thedata channel and their indexes, and controls the spreader 802 and asubcarrier mapper 803 depending on the determined ACKCH format. Thesubcarrier mapper 803, under the control of the ACKCH format controller806, applies the ACKCH symbols spread by the spreader 802 to inputs ofan IFFT 804, which are associated with REs of the ACKCH resources. Anoutput signal of the IFFT 804 is finally transmitted to a UE via anIntermediate Frequency (IF)/Radio Frequency (RF) stage.

FIG. 9 is a diagram illustrating a structure of a reception apparatus ofa UE of FIG. 7 according to the first embodiment of the presentinvention. A signal received at the UE from a base station is firstconverted into a frequency-domain signal by an FFT 901, and then appliedto an input of a subcarrier demapper 902. The subcarrier demapper 902receives an output of the FFT 901, and outputs spread ACKCH symbolscorresponding to ACKCH resources to be received. Since an ACKCHdemapping controller 905 can implicitly determine the ACKCH resourcesaccording to the number of RBs used for the previously transmitted datachannel and their indexes, the ACKCH demapping controller 905 controlsthe subcarrier demapper 902 and a despreader 903 according thereto. Thedespreader 903 despreads ACKCH symbols extracted by the subcarrierdemapper 902 and applies the despread ACKCH symbols to an ACK/NACKsymbol detector 904. The ACK/NACK symbol detector 904 determines whetherto transmit an ACK/NACK signal depending on the ACKCH signal despread bythe despreader 903.

The foregoing details described in the first embodiment of the presentinvention can also be applied to the case where ACKCH resources aremapped to CCEs as shown in FIG. 2B. That is, resources to be used forACKCH transmission are determined according to indexes of CCEs used fortransmission of a downlink control channel where a data channel isscheduled for the UE. In the mapping structure of FIG. 3 and thetransmission/reception procedures of FIGS. 6 and 7, when the CCEsallocated to the control channel are applied in place of the RBsallocated to the data channel, the details described in this firstembodiment can be applied in the same way.

Although a description of the first embodiment of the present inventionhas been given for allocation of downlink ACK/NACK physical channelresources for uplink data channels, the same can be applied even forallocation of uplink ACK/NACK physical channel resources for downlinkdata channels when an OFDM transmission technology is applied in theuplink. In addition, when resources are allocated to the data channel inunits of two RBs rather than one RB, one ACKCH resource is mapped to twoRBs in FIGS. 2A and 2B. Accordingly, the present invention can beapplied in units of physical resources allocated to data channels.

A second embodiment of the present invention applies the ACKCH resourceallocation method shown in FIG. 3 to uplink MU-MIMO.

MU-MIMO refers to the case where more than two different users aresimultaneously allocated the same RBs for data channel transmission.Generally, a base station orders two users having a low spatial channelcorrelation to transmit the same RBs over data channels, and thereception apparatus of the base station successfully decodes the datachannels received from the two users, thereby improving utilizationefficiency of uplink physical resources.

FIG. 10 is a diagram illustrating a format example of a schedulingchannel for uplink MU-MIMO transmission according to the secondembodiment of the present invention. A base station transmits thescheduling channel having the format of FIG. 10 to a UE. UE ID field1000 indicates ID information of a UE undergoing channel scheduling.Resource allocation information for transmission of a data channel iscarried on a resource indication field 1001, Transport Format (TF)information such as Modulation and Coding Set (MCS) level and payloadsize is carried on a Transport format field 1002, and HARQ-relatedinformation such as HARQ redundancy version and process number iscarried on an HARQ information field 1003. A value of 0 or 1 is set in aMU-MIMO UE flag bit field 1004 for a UE receiving the schedulingchannel. That is, the scheduling information is transmitted to two UEsperforming MU-MIMO transmission on the same RBs, and the field 1004 isdifferently set to 0 and 1 separately for the two UEs.

Therefore, regarding a UE for which the MU-MIMO UE flag bit field 1004is set to 0 and a UE for which the MU-MIMO UE flag bit field 1004 is setto 1, data channels undergo MU-MIMO transmission through the same RBsbut pilot signals for channel estimation for the data channels aremapped to orthogonality-satisfied physical resources before transmissionso the base station can receive the pilot signals from the two UEswithout mutual interference. Further, for the data packets received fromthe two UEs, ACKCHs transmitted in the downlink are also set such thatthey can be transmitted to the two UEs without mutual interference.

Aside from the fields 1000˜1004, additional information can betransmitted on the scheduling channel, and the present invention has nolimitation on transmission of the additional information. Although theembodiment considers the case where two UEs simultaneously make MU-MIMOtransmission on the same RBs, the same can be applied even to the casewhere N arbitrary UEs simultaneously make MU-MIMO transmission. Forexample, when MU-MIMO transmission is allowed for a maximum of four UEs,the MU-MIMO UE flag is composed of 2 bits to separately designate fourusers. When MU-MIMO transmission is allowed for a maximum of N UEs, theMU-MIMO UE flag is set to have log₂(N) bits. When log₂(N) is not aninteger, the MU-MIMO UE flag preferably has bits, the number of which isthe minimum integer greater than log₂(N).

In order to allow ACKCHs transmitted to the two UEs to be transmittedwithout mutual interference, for MU-MIMO transmission, more than two RBsare assumed to be allocated herein, and two UEs are assumed herein tosimultaneously transmit data channels on the more than two same RBs.Similarly, when N UEs make MU-MIMO transmission, more than N RBs areassumed herein to be allocated.

FIG. 11 illustrates an ACKCH transmission procedure of a base stationaccording to the second embodiment of the present invention. In theprocedure of FIG. 11, for MU-MIMO transmission, more than two RBs areassumed to be allocated, and two UEs simultaneously are assumed totransmit data channels on the more than two same RBs. With reference toFIG. 11, a description will be made of an ACKCH allocation procedureapplied separately to each MU-MIMO user. In step 1100, a transmissionapparatus of the base station determines whether to and prepares totransmit an ACK/NACK signal depending on the decoding result on a datachannel for a corresponding UE. In step 1101, the base stationdetermines whether a MU-MIMO UE flag bit field 1004 of the schedulingchannel received from the UE is set to 0 or 1. If the base stationdetermines in step 1101 that the MU-MIMO UE flag bit field 1004 is setto 0, the base station proceeds to step 1102 where the base station mapsa transmission ACK/NACK signal to ACKCH resource mapped to the smallesteven index among the RBs allocated to the UE. However, if the flag bitis set to 1, the base station proceeds to step 1104 where the basestation maps the transmission ACK/NACK signal to ACKCH resource mappedto the smallest odd index among the RBs allocated to the UE. In step1103, the base station multiplies the ACK/NACK signal mapped to theACKCH resource by a sequence to be applied to the ACKCH resource. Instep 1104, the base station finally maps the ACK/NACK signal multipliedby the sequence to IFFT inputs of the transmitter corresponding to themapped ACKCH resource before transmission.

Although the flag bit 0 is mapped to the ACKCH resource mapped to thesmallest even index among RBs and the flag bit 1 is mapped to the ACKCHresource mapped to the smallest odd index among RBs in this embodiment,the embodiment can alternatively be applied to the opposite case.

Therefore, the ACKCH resources mapped to consecutive RBs are set to usedifferent frequency resources as shown in FIG. 3, and ACKCHs allocatedto two MU-MIMO UEs are transmitted using the different frequencyresources according to the value of the MU-MIMO UE flag bit field 1004as described in the procedure of FIG. 11, making it possible to alwaysprevent interference from occurring regardless of the power differencebetween ACKCHs transmitted to the two UEs.

FIG. 12 is a diagram illustrating an ACKCH reception procedure of a UEaccording to the second embodiment of the present invention. In step1200, a UE prepares to receive ACKCH from a base station aftertransmitting a previously scheduled data channel. In step 1201, the UEdetermines from which ACKCH resource the UE will receive the ACKCHaccording to the value of a MU-MIMO UE flag bit field 1004 of ascheduling channel for the data channel. When the value of the MU-MIMOUE flag bit field 1004 is 0, the UE receives in step 1202 an ACKCHsignal from FFT outputs of the receiver corresponding to ACKCH resourcemapped to the smallest even index among the RBs allocated to the UE.However, if the value of the MU-MIMO UE flag bit field 1004 is 1, the UEreceives in step 1204 an ACKCH signal from FFT outputs of the receivercorresponding to ACKCH resource mapped to the smallest odd index amongthe RBs allocated to the UE. Thereafter, the UE despreads the receivedACKCH signal using a sequence applied to the ACKCH resource in step1203, and finally determines in step 1205 whether an ACK/NACK signal isreceived.

Although the ACKCH resource corresponding to the smallest even or oddindex is selected according to the value of the MU-MIMO UE flag bitfield 1004 in the foregoing transmission/reception procedure, otherrules can alternatively be established so frequency resources are usedas ACKCH resources transmitted to the two MU-MIMO transmission UEs, andthe present invention has no limitation thereon.

Regarding the MU-MIMO UE flag bit 1004, when data channels are notscheduled for MU-MIMO transmission, the base station can set the MU-MIMOUE flag bit 1004 to an appropriate value according to the need, therebycontrolling ACK/NACK resource allocation. For example, when the UE isallocated several RBs, ACK/NACK channels can be allowed to betransmitted on frequency resources where a less number of ACK/NACKchannels are allocated, using the MU-MIMO UE flag bit 1004.

The method described in the second embodiment can be applied even fordownlink MU-MIMO in the same way. In this case, a MU-MIMO UE flag bitfield is defined in a scheduling channel for a downlink data channel asshown by reference numeral 1004 of FIG. 10, and the base station sets adifferent value for the MU-MIMO UE flag bit field in each schedulingchannel being transmitted to two UEs allocated to the same RBs. Thus, inMU-MIMO, when more than two RBs are allocated to a data channel, the UEtransmits an ACK/NACK channel on resources corresponding to the MU-MIMOUE flag bit value among the ACK/NACK channel resources mapped to theRBs.

As is apparent from the foregoing description, the present inventionmaps ACKCHs mapped to consecutive RBs or consecutive CCEs, to differentfrequency resources, so REs used for transmission of the ACKCHs areuniformly distributed over the entire system band, making it possible toachieve high frequency diversity gain and inter-cell interferencediversity gain and improve ACKCH performance even in MU-MIMO.

In addition, the present invention contributes to a decrease in thenumber of unnecessary data retransmissions by improving ACKCHperformance, and an increase in the system capacity by improvingretransmission probability for the data channel failed in its normalreception.

While the invention has been shown and described with reference tocertain preferred embodiments thereof, it will be understood by thoseskilled in the art that various changes in form and details may be madetherein without departing from the spirit and scope of the invention asdefined by the appended claims.

1. A method for allocating physical resources to an Acknowledgement(ACK)/Negative Acknowledgement (NACK) signal channel representative of aresponse signal in a wireless communication system, the methodcomprising: grouping ACK/NACK signal channels corresponding to aplurality of resource blocks used for transmission of a data channel ora control channel into a plurality of groups so ACK/NACK signal channelshaving consecutive indexes do not belong to the same group; andallocating same frequency resources to ACK/NACK signal channelsbelonging to the same ACK/NACK signal channel group and allocatingorthogonal sequences so ACK/NACK signal channels in each ACK/NACK signalchannel group are distinguished in a code domain.
 2. The method of claim1, wherein a number of ACK/NACK signal channel groups has a maximumvalue obtained by dividing a number of resource blocks used fortransmission of the data channel, by four.
 3. The method of claim 1,wherein a sequence is defined by multiplying an orthogonal sequence by acell-specific random sequence.
 4. The method of claim 1, wherein powerbetween the ACK/NACK signal channel groups is constant.
 5. The method ofclaim 1, wherein the resource blocks are consecutive frequencyresources.
 6. The method of claim 5, wherein a number of ACK/NACK signalchannel groups has a maximum value obtained by dividing a number ofresource blocks used for transmission of the data channel, by four. 7.The method of claim 5, wherein a sequence is defined by multiplying anorthogonal sequence by a cell-specific random sequence.
 8. The method ofclaim 5, wherein power between the ACK/NACK signal channel groups isconstant.
 9. The method of claim 1, wherein the resource blocks are samefrequency resources allocated to a plurality of terminals.
 10. Themethod of claim 9, wherein a number of ACK/NACK signal channel groupshas a maximum value obtained by dividing a number of resource blocksused for transmission of the data channel, by four.
 11. The method ofclaim 9, wherein a sequence is defined by multiplying an orthogonalsequence by a cell-specific random sequence.
 12. The method of claim 9,wherein power between the ACK/NACK signal channel groups is constant.13. A method for allocating physical resources to an Acknowledgement(ACK)/Negative Acknowledgement (NACK) signal channel representative of aresponse signal in a wireless communication system, the methodcomprising: decoding a data channel and a control channel receivedthrough a plurality of resource blocks; generating an ACK/NACK symbolaccording to success/failure in the decoding; grouping ACK/NACK signalchannels corresponding to the resource blocks into a plurality of groupsaccording to a number of and indexes of the resource blocks so ACK/NACKsignal channels having consecutive indexes do not belong to the samegroup; allocating same frequency resources to ACK/NACK signal channelsbelonging to the same ACK/NACK signal channel group and allocatingorthogonal sequences so ACK/NACK signal channels in each ACK/NACK signalchannel group are distinguished in a code domain; and multiplying thegenerated ACK/NACK symbol by a sequence allocated to an ACK/NACK signalchannel for transmitting the generated ACK/NACK symbol, to spread thegenerated ACK/NACK symbol.
 14. An apparatus for allocating physicalresources to an Acknowledgement (ACK)/Negative Acknowledgement (NACK)signal channel representative of a response signal in a wirelesscommunication system, the apparatus comprising: a channel decoder fordecoding a data channel and a control channel received through aplurality of resource blocks; an ACK/NACK symbol generator forgenerating an ACK/NACK symbol according to success/failure in thedecoding by the channel decoder; an ACK/NACK signal channel formatcontroller for grouping ACK/NACK signal channels corresponding to theresource blocks into a plurality of groups according to a number of andindexes of the resource blocks so ACK/NACK signal channels havingconsecutive indexes do not belong to the same group, allocating samefrequency resources to ACK/NACK signal channels belonging to the sameACK/NACK signal channel group, and allocating orthogonal sequences soACK/NACK signal channels in each ACK/NACK signal channel group aredistinguished in a code domain; and a spreader for multiplying thegenerated ACK/NACK symbol by a sequence allocated to an ACK/NACK signalchannel for transmitting the generated ACK/NACK symbol, to spread thegenerated ACK/NACK symbol.